1. Field of the Invention:
This invention relates to a color image sensing apparatus having a flash device.
2. Description of the Related Art:
FIG. 1(A) of the accompanying drawings shows by way of example the conventional arrangement for white balance adjustment. Referring to FIG. 1(A), a colorimetric circuit 9 is arranged to separate the light of a light source into color components (or three primary colors of red, blue and green in this instance) and to convert these color components into electrical signals. A control part 12 is arranged to produce a white balance control signal on the basis of signals obtained from the colorimetric circuit 9. An image sensor 4 is arranged to separate the image of an object into, for example, the three primary colors an to convert them into electrical signals. A B amplifier 6 is arranged to amplify the blue component of the object's image obtained from the image sensor 4. An R amplifier 5 is arranged to likewise amplify the red component of the object's image.
A signal processing part 7 is arranged to produce a given standard TV signal on the basis of the red and blue signals amplified by the R and B amplifiers 5 and 6 and also a green signal obtained from the image sensor 4. A reference numeral 10 denotes a flash device.
The conventional apparatus of FIG. 1(A) operates in a manner as described below with reference to FIG. 1(A):
The red, blue and green components of the light of a light source are converted by the colorimetric circuit 9 into signals KR, KG and KB. The control part 12 then obtains a ratio KR/KG between the red and green components and a ratio KB/KG between the blue and green components of the light of the light source from signals KR, KG and KB. Meanwhile, the object's image is likewise converted by the image sensor 4 into signals representing the three different color components thereof including red (R), green (G) and blue (B) components.
The term "white balance adjustment" means as well known to remove the influence of the light of a light source from light reflected by an object in such a way as to ensure that a white object can be reproduced in a white color. The white balance adjustment can be accomplished by multiplying the above stated R signal by the ratio KG/KR and the B signal by the ratio KG/KB. Therefore, the control part 12 is arranged to produce control signals to the B amplifier 6 and the R amplifier 5 for this purpose. The details of the operation of the control part 12 are as follows: Referring to FIG. 1(B), the outputs KR, KG and KB of the colorimetric circuit 9 are respectively supplied to logarithmic compression circuits 12-1, 12-2 and 12-3 which are included in the control part 12 for the purpose of effective use of the dynamic range and for facilitating the ensuing processes of the circuit. The logarithmic compression circuits 12-1, 12-2 and 12-3 produces signals logKR, logKG and logKB. The signals logKR and logKG are supplied to a differential device 12-4 while the signals logKB and logKG are supplied to a differential device 12-5. As a result, differential outputs log(KG/KR) and log(KG/KB) are obtained from these differential devices.
Normally, the above stated differential outputs are supplied via switches 12-8 and 12-9 to the R amplifier 5 and the B amplifier 6 for white balance adjustment.
In the event of shooting with flash light, a charge completion signal produced from the flash device 10 comes to shift the connecting positions of switches 12-8 and 12-9 to their contacts disposed on the side of constants 12-6 and 12-7 provided for the flash device. Then, constants logSR and logSB for flashing are supplied to the R amplifier 5 and the B amplifier 6 respectively. This arrangement ensures correct white balance adjustment even in the case of flash photography. Examples of the above described arrangement of the prior art are disclosed in U.S. Pat. No. 4,567,509 and U.S. Pat. No. 4,499,487 assigned to the assignee of the present invention.
The arrangement described presents no problem if the object is illuminated solely by flash light during the shooting process with flashing. However, in the event of an object environed by a bright light which gives a mixed illumination light consisting of the flash light and the ambient light, the white balance would be lost if the adjustment is made on the basis of a given constant provided for white balance adjustment. This problem becomes conspicuous especially in cases where the amount of flash light is small like in daylight synchronization, or fill-in flash, or where the ambinent light greatly differs from the flash light like in the case of the light of a fluorescent lamp.
Further, another problem with the conventional white balance adjustment device resides in that: The light of a fluorescent lamp has a great intensity of the green component and thus greatly differs in nature from various light sources which are black-body radiators. Further, a fluorescent lamp is seldom arranged to convergently illuminate an object. Besides, it has a relatively high degree of illuminance and tends to strongly affect the flash light illumination. To solve this problem, it has been practiced to change a white balance adjustment value over to a constant value upon detection of the light of a fluorescent lamp as disclosed in U.S. Pat. No. 4,595,946. Under such a condition, therefore, it has been hardly possible to make accurate white balance adjustment.